Study H_C – HV properties of WC-Co alloys with different microstructures

Measurement of magnetic parameters is a method for express product quality control in processing of WC-Co tool hardmetals. The coercivity value is often used to estimate the WC grain size and the hardness of the hardmetal, whereas the nature of the WC grain size distribution is often disregarded. H_C – HV properties of WC-Co hardmetals with different microstructures were studied. For production samples of WC – 10 % Co hardmetals, it is shown that H_C does not depend on the width of the WC grain distribution and is a function of the average size d_1.0. The hardness HV30, which is affected by the width of the WC grain distribution, is a function of the d_3.2 value. Based on the obtained relations, a H_C – HV property map is plotted, taking into account the width of the WC grain size distribution. The map shows that measuring only the coercivity value will introduce uncertainty in the estimated hardness in the 100 – 120 HV range. However, joint measurement of H_C and HV makes it possible to estimate the width of the WC grain size distribution in the hardmetal. Based on the analysis of experimental hardmetal samples with a carbon content near the lower boundary of the carbon window and sintered at a relatively low temperature, the formation of an unusual structure was observed featuring the uniformly distributed large cobalt lakes. In such a structure, the size distribution of Co lakes is bimodal and the average size of the lakes is not proportional to the average size of WC grains. Moreover the formation of such a structure does not affect the hardness of the hardmetal, but leads to a significant decrease in the coercivity. The results obtained can be used for industrial inspection of the WC-Co hardmetals properties, as well as in the interpretation of experimental data.

1. Brueckl H., Breth L., Fischbacher J., et al. Machine learning based prediction of mechanical properties of WC-Co cemented carbides from magnetic data only / J. Refract. Met. Hard Mater. 2024. Vol. 121. P. 106665. DOI: 10.1016/j.ceramint.2022.09.030

2. García J., Collado Ciprés V., Blomqvist A., Kaplan B. Cemented carbide microstructures: a review / J. Refract. Met. Hard Mater. 2019. Vol. 80. P. 40 – 68. DOI: 10.1016/j.ijrmhm.2018.12.004

3. Lamelas V., Rolland M., Walbrühl M., et al. Modelling the formation of detrimental phases in cemented carbides / Materials & Design. 2023. Vol. 228. N 1 – 3. P. 111823. DOI: 10.1016/j.matdes.2023.111823

4. Roebuck B., Bennett E. Phase size distribution in WC/Co hardmetal / Metallography. 1986. Vol. 19. N 1. P. 27 – 47. DOI: 10.1016/0026-0800(86)90005-4

5. Roebuck B., Mingard K., Jones H., et al. Aspects of the metrology of contiguity measurements in WC based hard materials / J. Refract. Met. Hard Mater. 2017. Vol. 62. P. 161 – 169. DOI: 10.1016/j.ijrmhm.2016.05.011

6. Aguirre M., Urreta S., Bercoff P. Microstructure dependence of magnetization mechanisms in Co-Fe thick films / J. Mater. Sci. 2022. Vol. 57. N 3. P. 1890 – 1901. DOI: 10.1007/s10853-021-06746-9

7. Herzer G. Soft magnetic nanocrystalline materials / Scr. Metall. Mater. 1995. Vol. 33. P. 1741 – 1756. DOI: 10.1016/0956-716X(95)00397-E

8. Xue D., Chai G., Li X., et al. Effects of grain size distribution on coercivity and permeability of ferromagnets / J. Magn. Magn. Mater. 2008. Vol. 320. P. 1541 – 1543. DOI: 10.1016/j.jmmm.2008.01.004

9. Roebuck B. Hardmetals hardness and coercivity property maps / NPL Report. MATC(MN). 2002. Vol. 14. P. 1 – 9.

10. Roebuck B. Extrapolating hardness-structure property maps in WC/Co hardmetals / J. Refract. Met. Hard Mater. 2006. Vol. 24. N 1 – 2. P. 101 – 108. DOI: 10.1016/j.ijrmhm.2005.04.021

11. Pesin V. A., Osmakov A. S., Boykov S. Yu. Properties of WC-Co hardmetals as a function of their composition and microstructural parameters / Powd. Metall. Func. Coat. 2022. Vol. 16. N 3. P. 37 – 44. DOI: 10.17073/1997-308X-2022-3-37-44

12. Mueller D., Konyashin I., Farag S., et al. A novel express method for determining WC grain sizes and its use for updating dependencies of coercivity and hardness on WC mean grain size in hardmetals / J. Refract. Met. Hard Mater. 2023. Vol. 117. P. 106416. DOI: 10.1016/j.ijrmhm.2023.106416

13. Engqvist H., Uhrenius B. Determination of the average grain size of cemented carbides / J. Refract. Met. Hard Mater. 2003. Vol. 21. N 1 – 2. P. 31 – 35. DOI: 10.1016/S0263-4368(03)00005-2

14. Vasilyeva M. V., Pesin V. A., Osmakov A. S., et al. Research of the depending of the hardness of WC-Co hardmetals on the nature of the distribution of WC grains by size / Industr. Lab. Mater. Diagn. 2023. Vol. 89. N 2(I). P. 45 – 49 [in Russian]. DOI: 10.26896/1028-6861-2023-89-2-I-45-49

15. Tarrago J., Coureaux D., Torres Y., et al. Implementation of an effective time-saving two-stage methodology for microstructural characterization of cemented carbides / J. Refract. Met. Hard Mater. 2016. Vol. 55. P. 80 – 86. DOI: 10.1016/j.ijrmhm.2015.10.006

16. Podor R., Le Goff X., Lautru J., et al. SEraMic: a semi-automatic method for the segmentation of grain boundaries / J. Eur. Ceram. Soc. 2021. Vol. 41. N 10. P. 5349 – 5358. DOI: 10.1016/j.jeurceramsoc.2021.03.062

17. Bashkov O. V., Kim V. A., Popkova A. A. Technique for digital image processing of the microstructure of aluminum alloys in the MATLAB / Industr. Lab. Mater. Diagn. 2013. Vol. 79. N 10. P. 34 – 39 [in Russian].

18. Kim V. A., Belova N. V., Zolotareva S. V. Quantitative indicators of the structural organization of polycrystalline materials / Industr. Lab. Mater. Diagn. 2014. Vol. 80. N 4. P. 43 – 46 [in Russian].

19. Betteridge W. The properties of metallic cobalt / Prog. Mater. Sci. 1979. Vol. 24. P. 51 – 142. DOI: 10.1016/0079-6425(79)90004-5

20. Bertalan C., Moseley S., Pereira L., et al. Influence of sintering parameters on the microstructure and mechanical properties of WC-Co hardmetals / J. Refract. Met. Hard Mater. 2024. Vol. 118. P. 106439. DOI: 10.1016/j.ijrmhm.2023.106439